Figure shows the angle at which the cutting edge enters the workpiece, the engage angle (E), and the angle at which it disengages the workpiece, disengage angle (DE). The engage and disengage angles are factors that determine the degree of impact that the cutting edge is exposed to when cut starts and finishes. The engage and disengage angles relate to tool life and need to be carefully considered.
When the diameter and amount of offset (position of the workpiece and the centre of the face mill) are determined, the engage and disengage angles will also be decided. This can be seen in the figure below (EA > EB).
If the engage angle (EA) is too large then the chip thickness at the point of entry could be less than the feed per tooth. If this is the case the inserts will rub, therefore the section being machined can be prone to plastic deformation.
This rubbing can lead to the cutting edge being exposed to high cutting forces leading to chipping and possiblefracturing. Meanwhile, if the engage angle (EB) is too small then the load on the cutting edge will also increase resulting in chipping and possible fracturing.